In recent years, progress is being made in research and development of diverse functional elements which involve the use of an organic semiconductor.
Organic EL elements are known as being one of the most common among such functional elements. An organic EL element is a current-driven light-emitting element, and commonly includes a pair of electrodes consisting of an anode and a cathode, and a functional layer containing organic material disposed between the pair of electrodes. The functional layer includes layers such as an organic light-emitting layer and a buffer layer. Further, there are cases where a hole-injection layer is disposed between the functional layer and the anode. The hole-injection layer is disposed for injecting holes to the functional layer. When driving the organic EL element, voltage is applied between the pair of electrodes. The emission of light from the organic EL element is caused by an electric-field light-emitting phenomenon taking place as a result of the recombination of holes which are injected from the anode to the functional layer, and the electrons which are injected from the cathode to the functional layer. Now, more attention is being given to the application of organic EL elements as a light-emitting element or a light source for various display devices. This owes to the advantageous characteristics of the organic EL element, which include: high visibility resulting from self-luminescence; and excellent shock resistance resulting from the fully solid-state structure thereof.
Organic EL elements can be largely divided into two types, according to the material used for forming the functional layer therein. The first type of organic EL elements is a vapor deposition type. A vapor deposition-type organic EL element has a functional layer that is mainly composed of organic low molecular material and that is formed as a film by applying a vacuum process such as a vapor deposition method. The second type of organic EL elements is an application type. An application-type organic EL element has a functional layer that is mainly composed of ink including either organic high molecular material, or organic high molecular material having an excellent thin film forming property, and that is formed as a film by applying a wet process in which the ink is applied and dried, such as an inkjet method and a gravure printing method.
Nowadays attempts are being made to realize the manufacturing of larger organic EL panels by using application-type organic EL elements. As already described in the above, a functional layer is formed by applying ink including specific material via a wet process in an application-type organic EL element. In the application of the wet process, the precision with which the application of functional layer material of the respective colors to corresponding positions on the substrate is performed is not influenced by the size of the substrate. Hence, the technical barrier to be overcome in realizing the manufacturing of larger organic EL panels is relatively low.